The present invention relates to fluent fuel burners, and more particularly to an improved impeller which provides the turbulence required for efficient combustion by compensating for changes in volume of the combustion air over the burner load range, or for differences in volume between the combustion air and other sources of oxygen.
Burners firing fluent fuels require considerable turbulence to achieve optimum combustion. Turbulence is generally the function of overall burner design and air-side pressure drop across the burner. The higher the pressure drop, the greater the turbulence. When a burner is designed for optimum combustion at full load, its pressure drop at 1/2 load is only 1/4 of the full load pressure drop, since air-side pressure drop is proportional to the square of the ratio of air flows.
The present state of the art provides an impeller of the type disclosed in U.S. Pat. No. 2,260,062 assigned to the assignee of the present invention and generally comprising a frusto-conical plate having a central opening for admitting a liquid fuel burner sprayer plate and including a series of blades formed by bending out portions of the plate leaving openings therethrough for the flow of air or other oxygen-bearing gaseous medium. The impeller is normally located within a frusto-conical section of the burner port and is movable along the burner axis to change the free flow area between the impeller and burner port thereby compensating for changes in volume of the combustion air or other oxygen-bearing gaseous medium flowing therethrough.
It has been found, however, that on wide range burners, a design providing optimum air-side pressure drop at the burner upper load range will experience a reduction in air-side pressure drop at the burner lower load range which is beyond the corrective adjustment available through change of impeller position with respect to the burner port.